AME 64:299-309 (2011)  -  DOI: https://doi.org/10.3354/ame01529

ABSTRACT: Dissolved organic matter (DOM) is an important source of organic carbon for sus­taining the growth of heterotrophic bacteria. We investigated the bacterial utilization of high-­molecular-weight (HMW; >30 kDa to 0.22 µm) and low-molecular-weight (LMW; >10 to 30 kDa) fractions of DOM. DOM was collected from a station in Dona Paula Bay, on the west coast of India, and fractionated into HMW and LMW portions. Each size fraction was inoculated with a natural population of bacteria and incubated over a period of 15 d at room temperature (28 ± 2°C); during this period, sub-samples were removed and the following were measured: dissolved organic carbon (DOC), total dissolved carbohydrate (TDCHO), free monosaccharide (MCHO), dissolved uronic acid (DURA), δ¹³C, bacterial abundance (BA), and bacterial production (BP). The LMW fraction was isotopically heavier (δ¹³C = −23.7 to −21.7‰) than the HMW fraction (δ¹³C = −27.0 to −26.2‰), and the initial TDCHO content of these fractions was 25 and 16%, respectively. The initial DURA content was similar in the LMW DOM (7.4% DOC) and the HMW DOM (7.0% DOC). BA and BP were consistently higher in the LMW DOM than in the HMW DOM. In 15 d incubation, greater proportions of DOC (35%), TDCHO (76%) and DURA (36%) were utilized in the LMW DOM than in the HMW DOM. This suggests that the LMW DOM was more biologically reactive, i.e. it was utilized more rapidly, than the HMW DOM. It appears that the bioreactivity and origin of the DOM strongly influenced its utilization by natural heterotrophic bacteria.

KEY WORDS: Dissolved organic matter · Size fractions · Carbohydrates · Polysaccharides · Bacteria · Bacterial production · Dona Paula Bay